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The structural, elastic, electronic and optical properties of K 2 CuBiX 6 (X ​= ​Br, Cl) are studied by the first principle calculation in this paper. Their structural and thermodynamic stabilities are guaranteed by the formation energy, binding energy and Born-Huang criterion. The results of elastic constants show that the two materials are ductile and can be applied in foldable optoelectronic devices. Besides, The calculated bandgap values are 1.03 ​eV and 1.44 ​eV for K 2 CuBiBr 6 and K 2 CuBiCl 6 , respectively, which is just in the ideal energy gap range of semiconductors. K 2 CuBiX 6 has very small effective mass advantageous to carrier transport. In addition, the optical properties analysis shows that K 2 CuBiX 6 has excellent light absorption properties in ultraviolet–visible wavelength. Due to their suitable bandgaps and good light absorption, K 2 CuBiX 6 has a promising application in solar cells and other optoelectronic devices. In this study, the perovskites K 2 CuBiX 6 (X ​= ​Br, Cl) are proposed as functional materials in solar cells. [Display omitted] • The K 2 CuBiX 6 (X ​= ​Br, Cl) are very suitable for photosensitive materials of solar cells. • The K 2 CuBiX 6 can be a potential candidate for excellent light absorbing material. • The K 2 CuBiX 6 is the structural and thermodynamic stabilities. [ABSTRACT FROM AUTHOR]

The post-transition metal cations are widely used in rechargeable batteries, solar-cells, and birefringent compounds. In this paper, the electronic structures and birefringence of ternary CsSnX 3 (X ​= ​Cl, I), CsPbX 3 (X ​= ​Cl, Br, I), and binary MX 2 (M ​= ​Sn, Pb; X ​= ​Cl, Br) compounds are investigated using the first-principles methods. The results show that these metal halides own different mechanism in stereochemical activity and birefringence, i.e., the stereochemical activity of lone-pair electrons are determined by energy difference between cation s states and halogen p states, and the stereochemical activity decreases from Cl to I. While the cation p states play an important role in determining the birefringence, and the birefringence increased from Cl to I. [Display omitted] • Electronic structures and optical properties of post-transition metal halides are investigated. • Stereochemical activity of lone-pair electrons are determined by energy difference of cation-s and halogen-p states. • Cation p states play an important role in determining the birefringence. [ABSTRACT FROM AUTHOR]

In this paper, we study theoretically the structural, electronic, optical, elastic and thermoelectric properties of MgSc 2 X 4 (X ​= ​S; Se) compounds using first-principles calculations. The calculated band structure reveals that MgSc 2 S 4 and MgSc 2 Se 4 are direct-gap semiconductors. The optical features of MgSc 2 S 4 and MgSc 2 Se 4 as functions of photon energy were calculated for energy range of 0–20 ​eV. MgSc 2 X 4 (X ​= ​S; Se) are promising optoelectronic, and thermoelectric compounds whose absorption rates can reach 4 orders of magnitude in the visible range, and 6 orders of magnitude in ultraviolet range. Both chalcogenides possess high brittleness with the Pugh's ratio (B / G), and Cauchy pressure C 12 − C 44 of 1.60 and − 4.485 GPa (for MgSc 2 Se 4); 1.61 and − 3.655 GPa (for MgSc 2 S 4). MgSc 2 S 4 and MgSc 2 Se 4 reveal similar Z T e values. The obtained properties of MgSc 2 X 4 (X ​= ​S; Se) are well confirmed by experimental results. Weighted band structures of MgSc 2 S 4 and MgSc 2 Se 4 as obtained by TB-mBJ. Image 1 • Structural, and electronic properties of MgSc 2 X 4 (X ​= ​S; Se) spinel compounds. • The distribution of the conduction bands depends on the hybridization S/Se- p orbitals and Sc- d orbitals. • High absorption rate in the visible and ultraviolet ranges. • High brittleness of MgSc 2 S 4 , and MgSc 2 Se 4. • Good thermoelectric and optoelectronic properties. [ABSTRACT FROM AUTHOR]